Radioscopic and radiographic apparatus suppressing the effect of secondary rays



March 24. 1925. 1530937 L. E. GUNTHER RADIOSCOPIC AND RADIOGRAPHIC APPARATUS SUPPRBSSING THE EFFECT OF SECONDARY RAYS Filed Sept. 5, 1921 0 Fig. I.

Inventor: Louis E. Gunther,

by M M Has Attorney.

Patented Mar. 24, 1925;

UNITED STATES PATENT OFFICE.

LOUIS EMILE GUNTHER, or PARIS, FRANCE, assronon T0 GENERAI". ELECTRIC com- PANY, A CORPORATION OF NEW YORK.

RADIOSCOPIC AND RADIOGRAIHIC APPARATUS SUPPBESSING THE EFFECT OF SEC- ONDARY RAYS.

Serial No. 498,543.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT. L, 1313.)

To all whom it may concern:

Be it known that I, LOUIS EMILE GUN- THER, citizen of the Republic of France, residing at 23 Rue Casimir Perier, Paris, France, have invented new and useful Improvements in Radioscopic and Radiographic Apparatus suppressing the Effect of Secondary Rays (for which I have filed an application in France, March 31, 1914,

Patent No. 476,033), of which the following.

is a specification.

It is known that X rays give rise to the so called secondary rays when they meet with bodies which offer certain resistance to them. In the case of fluoroscopic or radiographic work, these secondary rays act upon the screen or the plate at the same time as the main rays and decrease the distinctness of the picture.

Some tests have been made to improve the distinctness of the picture by opposing the secondary rays to prevent them from acting upon the screen or the plate. For this purpose, apparatus called Filters have been used consisting of lead partitions parallel to each othert0 form a number of adjacent quadrangular cells. Such devices stop most of the more or less slanting secondary rays and admit only the X rays which are nearly parallel to the partitions.

These filters are satisfactory when radiographing very thick bodies to show the small details or to detect very small foreign parts, but they have a serious drawback in that the picture is partially covered by the shade of the filter. This shade makes observation difficult, and sometimes completely conceals the thing to be observed which is a very serious fault.

In accordance with the present invention I have provided an improved apparatus for screening or intercepting the secondary rays and admitting to the plate or screen only the X rays coming directly from the source, thus giving a perfectly distinct picture, even in the case of a thick body, and at the same time preventing the filter from producing a shade on the screen or on the plate.

The accompanying drawing shows diagrammatically in Fig. 1, the relation of an X-ray tube to a ray filter embodying mv invention; and Fig. 2 shows in perspective, a belt embodying my invention mounted upon driving rolls geared to a motor.

Referring to Fig. 1, the invention provides a filter 1 of suitable design between the body 2, submitted to the X rays from an X-ray tube 3, and the screen or the plate 4, and to continuously move this filter during the whole duration of the exposure, in order that the shade which is produced at a given time is moved all the time and leaves no definite mark. The only objectionable result is a decrease in the action of the X rays which is easy to compensate for by lengthening the duration of the exposure.

The invention consists also in using a form of filter and a law of motion which bear to each other such a relation that the decrease in the effect of the X rays due to the filter is evenly distributed on the surface of the screen.

If, in the practice of the invention, a filter having rectangular cells is used, it is necessary to give it a linear motion with uniform speed and, preferably, in the direction of the diagonals, as shown in Fi 2, in order to obtain an even effect of the X rays over the entire surface of the plate.

If the operation is of appreciable length, a long filter would be required to permit continuous movement at a required rate. In such a case, it is therefore advisable to give the filter the form of an endless chain consisting of movable elements, or the form of an endless belt consisting of wire gauze. As illustrated in Fig. 2, I prefer to employ a wire-gauze having square wires the dimensions of which are equal to the intervals between them. The thickness of the gauze can be as small as necessary to ensure the necessary flexibility of the device, under the condition that the ratio between the height and the width of the cells is kept good. Experience has shown that secondary rays can be satisfactorily avoided when the height of the cells is about the same as their width.

The chain or the endless belt 5 which constitutes the filter, is supported by a pair of driving rolls 6, 7 located on each side of the plate. and Hm upper art at ska be the belt asses in front of the plate 4 A source 0 power for driving the rolls is re resented b a motor 8.

Vhen the -ray bulbs are supplied by a coil, the emissions of X rays are not continnous.

Therefore, if the filter is moved ve slowly, the emissions of current will pro uce on the late a number of distinct pictures of the lter. It is easy to understand that in such a case the speed of the filter m'ustbe hi h enough to revent this trouble.

iinally, the filler can be made from a metallic sheet into which the cells are unched.

It is obvious that it is referab e to use for the filter, elements whic will be located to suit the direction of the X rays. Therefore, the partitions-must theoretically converge all towards the emitting center of these rays.

Practlcall if the distance between the source of rays and the plate is great enough as compared with the dimensions of the cells of the filter, these converging partitions are not absolutel necessary.

While I have descri ed my invention as referring more particularly to the exposed plate in the caseof radiography, it is my intention to cover this system for the use of radioscopy. In this latter case, the filter must be moved fast enou 'h in order that its shade becomes unnoticeafile at an time and that it produces only a decrease in the illu-' mination. V

It must be remarked also that instead of an uniform and continuous motion, an alternate motion can be used in certain cases.

The above description is given as an ex ample only, the forms, dimensions and details of the apparatus, can be varied without changing the general design of the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An X-ray apparatus for suppressing the shadowing effect of secondary rays comprising a screen and supporting means thereor, permitting linear displacement of said screen when operatively mounted with rc- X-ray source and phgtographic of a useful beam of primary rays, an means for giving said screen a linear displacement durin an exposure interval.

3. n X-ra screen for suppressin the eilect of secon ry rays comprising a urality of articulated elements havin wal s substantially opaque to X-rays an extending in the general direction of X-rays to be transmitted, said elements constituting a. belt and means for giving said belt a linear displacement.

4. An X-raylscreen comprising a plurality of substantia y rectangular cells havi v walls-substantially opaque to X-rays a d means for linearly dislplacing said screen in a direction at an ang c with respect to the walls of said cells.

5. An X-ray screen comprising a belt-con sisting of a plurality of cells having walls substantially opaque to X-rays, and a set of driving rolls for said belt.

An X-l'fly screen comprising a belt composed of walls spaced apart a distance about equal to their height and driving rolls for said belt. 4

7. An X-ray screen comprising a plurality of rectangular cells and means for movingsaid screen in the direction of the diagona s of said cells,

8. The method of avoiding shadows on a photographic plate or film by a screen havmg a lurality of partitions opa ac to X rays. wiich consists in moving said screen during the exposure interval in a direction which will carry said partitions across said plate or film.

LOUIS ELHLE' GUNTHER. 

